Distance and speed controllers for motor vehicles are known in the art and are also referred to as ACC (“adaptive cruise control”) systems. In these systems, objects such as vehicles ahead that are in the same traffic lane in which the controlled vehicle is traveling are detected using a locating system. The locating system can be a camera system or a radar system, using which the distance to the vehicle ahead and the relative speed can be measured. By using a direction-sensitive radar system or by relying on additional parameters such as the steering angle of the vehicle, the detected objects can be checked for plausibility so that, for example, vehicles in the vehicle's own lane can be distinguished from traffic signs or markings on the side of the road or from vehicles in other lanes. If a vehicle ahead in the same lane is within the locating range of the radar, the driving speed of the controlled vehicle is regulated through intervention in the vehicle's drive and braking systems such that a speed-dependent margin of safety from the vehicle ahead is maintained. If, on the other hand, there is no vehicle within the locating range in the same lane, then regulation to a speed desired by the driver, which has been entered using a set command, is effected. An example of a regulating system of this type is described in “Adaptive Cruise Control System—Aspects and Development Trends” by Winner, Witte, Uhler and Lichtenberg, Robert Bosch GmbH, in SAE Technical Paper Series 961010, International Congress & Exposition, Detroit, Feb. 26-29, 1996.
Such ACC systems were generally used previously in relatively stable traffic situations, which are characterized by relatively high vehicle speeds and correspondingly large distances between vehicles, especially during travel on superhighways or expressways. If the vehicle being tracked as the target object decelerates to a standstill in a traffic jam, for example, and the speed of the vehicle equipped with the ACC system is also decreased accordingly, then the speed controller automatically shuts off at a specific limiting speed on the order of magnitude of about 20 km/h, and an acoustic prompt is issued to the driver to take over the control of the vehicle and to decelerate the vehicle to a standstill. The reason for this shutoff is primarily that the detection range of the locating system has gaps in the close range so that, as the distances from the target objects decrease, the danger increases that an obstruction will not be detected and recognized, even if it is in the same traffic lane.
For example, the detection range in radar systems is limited by the geometry of the radar beam, which emanates divergently from the radar sensor and scans only a limited angle range so that the full width of the traffic lane is not detected until a certain distance in front of the vehicle is reached. Similar “blind spots” can also occur in camera systems or other known locating systems.
An object of the present invention is to provide a speed controller that makes it possible to expand the range of application of the regulating function to include low speeds, without having to make exaggerated demands on the detection range of the locating system.